In a blender blend cream, milk, and mint until mint is finely
chopped. In a saucepan bring cream mixture just to a boil and cool 15 minutes. Whisk in egg and sugar and cook over moderate heat, stirring constantly, until slightly thickened and about 170°f on a candy or meat thermometer. (Do not let boil or it will curdle.)
Pour custard through a fine sieve or strainer into a bowl. Cover the surface with plastic wrap so that it is not exposed to air and chill until cold, at least 3 hours. Can be made to this step up to a day ahead.
Freeze custard in an ice cream maker - I recommend the Donvier if you're in an apartment - it's small and works quickly without the fuss of ice and salt.
Transfer ice cream to a container and put in freezer to harden.
To serve, garnish with fresh mint tops, berries, or chopped dark chocolate.